1. Field of the Invention
The present invention relates to a linear-motion rolling guide unit with a flange cover, in which a slider is mounted slidable on a track rail having longitudinally extending raceway grooves, with a number of balls interposed between the slider and the track rail.
2. Description of the Prior Art
A ball spline, in which a slider is linearly moved along a ball spline shaft with balls held in a retainer rolling between the slider and the shaft, has found applications in industrial robots and transfer machines. The ball spline forms a linear-motion rolling guide unit (a kind of bearing) and includes an elongate ball spline shaft and a slider slidable on the ball spline shaft and receiving rotary torque from the ball spline shaft.
A known example of the ball spline with a retainer is a linear-motion ball bearing. The linear-motion ball bearing comprises mainly an outer cylinder, a retainer, balls as rolling elements, and retainer rings. The retainer has formed in its outer circumference circuit-like circulation passages for endlessly guiding the circulating balls. The inner surface of the outer cylinder is formed with raceway portions where the balls are loaded while rolling, inclined surfaces for smoothly circulating the balls from the raceway portions to unloaded escape portions, and circumferentially inclined rounded surfaces forming return passages for the balls (see Japanese Patent Laid-Open No. 187112/1984).
Another known example of the ball spline is one that has a flange provided to the outer cylinder to allow the ball spline to be secured to a mount such as housing, case and frame. This ball spline comprises an elongate guide shaft, a bearing cylinder body loosely sleeved over the guide shaft so that it is slidable on the guide shaft, a retainer interposed between the flanged bearing cylinder body and the guide shaft to hold the balls, and a flange secured to the bearing cylinder body by nickel brazing (see Japanese Utility Model Laid-Open No. 87328/1993).
For the ball spline to be securely installed on a mount such as housing, case and frame, as described above, a structure is known in which a flange is fixed, as by welding, to the end of the outer cylinder that forms the slider in the ball spline. The ball spline that fixes the flange to the outer cylinder, however, requires the outer cylinder or the flange to be machined into a shape or structure that allows fixing of the flange to the outer cylinder. It is also necessary to machine the outer cylinder and the flange to a high precision for securing them together and to fix the flange to the outer cylinder firmly, which in turn increases the manufacture cost.